In a semiconductor device manufacturing process, various processes such as a film formation, an etching and so forth are repeatedly performed on a substrate such as a semiconductor wafer. As a semiconductor manufacturing apparatus of performing such processes, a substrate processing system in which a plurality of processing devices for performing different processes is installed, is used. Such a substrate processing system includes one or more substrate transfer devices to transfer a substrate inside the system including between the plurality of processing devices, and delivery the substrate between the system and other substrate processing system.
Such a substrate transfer device includes a transfer arm which is capable of performing operations such as bending and stretching, swing, elevating, linearly-moving and the like. In addition, the substrate transfer device transfers the substrate while holding the substrate using a support part installed in a leading end of the transfer arm.
During the transfer, due to various factors, a substrate may not exist in the support part, or the substrate may be transferred while being misaligned from a predetermined position of the support part. When the substrate does not exist or when the substrate is deviated from a permissible range in the support part, it is difficult to accurately transfer the substrate inside the substrate processing system, e.g., between the processing devices and the substrate transfer devices, or deliver the substrate between the substrate processing system and the other substrate processing system. This reduces the accuracy of the processes such as the film formation, the etching and so forth, and throughput, which causes a reduced yield. In addition, the excessive misalignment may cause some damages to the substrate by colliding with a member along a transfer path or being dropped down from a holding member, in the course of the transfer.
There is known a technique in which an optical sensor is used to detect a presence or absence of a substrate or a misalignment thereof in a support part in the course of the transfer. For example, there is proposed a method of irradiating light along an optical axis perpendicular to a surface of a circular substrate which is being transferred, detecting a change in signal when the circular substrate traverses through the optical axis, converting the change in signal into coordinates to obtain a central coordinate of a virtual circle, and calculating an amount of misalignment of the substrate.
There are also proposed techniques for irradiating light along an optical axis inclined with respect to a surface of a substrate which is being transferred, and detecting a presence or absence of the substrate or a misalignment thereof. However, in a case where a plurality of substrates is transferred while being held in multi-stage processing, such techniques require a plurality of optical sensors which is installed individually for every substrates held in each multi-stage processing.
That is to say, in the case where the plurality of substrates is transferred while being held in multi-stage processing, individual optical sensors are installed with respect to the respective substrates to find out positions of the respective substrates in the course of the transfer. This requires a space in which the individual optical sensors are installed and increases a cost for installing, thus resulting in an overall increase in footprint or an increased cost. In particular, there are significant limitations in arranging the plurality of optical sensors in a limited transfer space of the substrate processing system by the number of the substrates.